1. Field of the Invention
The present invention relates to a numerical control feed device for use in a machine tool, preferably, of the type that machines workpieces of an oval or elliptical cross section such as automotive camshafts.
2. Discussion of the Prior Art
A method has been known heretofore wherein feed movement of a grinding wheel in a direction perpendicular to the axis of a work spindle is controlled by a numerical controller in synchronous relation with rotation of the work spindle to grind a workpiece such as automotive camshaft or the like. In this method, profile data have to be supplied to the numerical controller in order to effect the synchronous control of feed movement of the grinding wheel. The profile data prescribe the feed movement of the grinding wheel per unit angle rotation of the work spindle so that the grinding wheel performs profile generating motion involving reciprocative movement following a desired finish shape of the workpiece.
Further, in order to grind the workpiece, machining cycle data which control feed, cut-in feed, retraction movement and so forth of the grinding wheel have to be prepared in addition to the profile data. The workpiece is machined when rotation of the work spindle and feed movement of the grinding wheel are numerically controlled in accordance with the machining cycle data and the profile data. In particular, the machining accuracy of the workpiece depends largely upon the ability of a work spindle axis and a grinding wheel feed axis to accurately follow command data or signals. Thus, increasing the gains of servo amplifiers in the feed servo systems may be conceived to reduce errors due to following delays. However, this solution cannot be taken because of causing instability in servo control.